1. Field of Invention
The present invention relates to a method and device for treating a substrate, and more particularly to a substrate, thermal treatment assembly and method of operating the thermal treatment assembly for performing a thermal treatment process on the substrate.
2. Description of Related Art
In material processing methodologies, pattern etching comprises applying a thin layer of radiation-sensitive material, such as photoresist, to an upper surface of a substrate, patterning this thin layer of radiation-sensitive material using photolithography to form a pattern therein, and transferring the pattern to the underlying material film using an etching process. Photolithographic systems for performing the above-described material processing methodologies have become a mainstay of semiconductor device patterning for the last three decades, and are expected to continue in that role down to 65 nm resolution, and less.
The patterning of the radiation-sensitive material generally involves coating an upper surface of the substrate with a thin film of radiation-sensitive material, and then exposing the radiation-sensitive material to a geometric pattern of electro-magnetic (EM) radiation using, for example, a photolithography system, followed by the removal of the irradiated regions of the radiation-sensitive material (as in the case of positive photo-resist), or non-irradiated regions (as in the case of negative resist) using a developing solvent.
Moreover, throughout the coating, exposing and developing processes, the radiation-sensitive material is thermally treated several times during the preparation of the pattern in the thin layer of radiation-sensitive material. For example, the radiation-sensitive material is baked following the application of the material to the substrate (i.e., post-application bake, PAB), and also the radiation-sensitive material is baked following the exposure of the material to EM radiation (i.e., post-exposure bake, PEB). Further yet, the radiation-sensitive material undergoes a hard bake following the developing of the pattern to remove residual developing solvent.
One of the more critical thermal treatments during the preparation of the photoresist mask is the PEB. One reason for this criticality includes the observation that this treatment affects the uniformity of the critical dimension (CD) of the pattern formed in the photoresist mask across the substrate. With the current use of chemically amplified resists (CAR), these resists undergo a catalytic reaction upon exposure to the thermal treatment which causes acid diffusion that, in turn, affects the CD during the subsequent developing process. As a result, variations in the CD across the substrate are strongly affected by spatial variations in substrate temperature.
Often times, this sensitivity of the CD to spatial temperature variations is referred to as PEB sensitivity in the lithography community. For example, current ArF resists have a PEB sensitivity of approximately 1 to 5 nanometers (nm) per degree C. temperature variation. As a result, the relationship between variations in the substrate temperature and the acid diffusion rate/distance and, hence, variations in the CD require strict control of the uniformity of the substrate temperature, particularly during the PEB.